It would be slightly better. The biggest difference between the two cans is that the MDR-7506 comes with a five year warranty, four years longer than the MDR-V6's. However, considering that one of the reasons these headphones are so great is that they don't break, and since they're only $70 to begin with, paying $30 for four extra years of warranty doesn't seem smart.
Other than that, the only non-cosmetic difference is the plug. The nickel-plated plug on the MDR-V6 will not corrode unless you are into underwater headphone listening. The MDR-7506's gold plug has little other benefit, unless you constantly twist it in the jack as you listen -- the gold plug has slightly better microphonic reduction when it's being moved.
So, no, it's not worth it to get the MDR-7506 over the MDR-V6 if they're both available to you. Well, unless you like blue a lot better than red or the word "professional" better than the phrase "for digital."
kerely